The overall goal of this project is to understand the structure and function of highly functional membranes using a combination genetic, molecular, and photosynthetic techniques. Specifically, we are interested in studying the effect of perturbing conditions such as mutation or viral infection on the function of photosynthetic membranes. We have so far isolated 80 temperature-sensitive mutants in the blue-green algae that fall into 2 groups. Some are not able to grow at 40 degrees C, while others are able to grow slowly at 40 degrees C, but are highly fluorescent. We have begun to characterize a few of the mutants from this later group. Their growth rates are usually the same as wild-type at 30 degrees C, but only one-half to one-third that of the wild-type. The most completely characterized mutant has room-temperature and liquid N2 absorption spectra that are identical to the wild-type spectra under most conditions. The room temperature emission spectra are also identical. However, the room temperature fluorescence kinetics of the mutant are changed, especially in the presence of the inhibitors DCMU and DBMIB. Acrylamide gel electrophoresis shows that the mutant is deficient in one band and gives rise to a lower molecular weight component. Comparison of PSII and PSI fragments show that the mutant has certain spectral differences in the PSII fraction. BIBLIOGRAPHIC REFERENCES: Sherman, L.A., Connelly, M. and Sherman, D.M. (1976). Infection of Synechococcus cedrorum by the Cyanophage AS-IM. I. Ultrastructure of Infection and Phage Assembly. Virology, Feb. 1976. Sherman, L.A. and Pauw, P. (1976). Infection of Synechococcus cedrorum by the Cyanophage AS-IM. II. Protein and DNA Synthesis. Virology, Feb., 1976.